1. Field of the Invention
The present invention relates to a lens barrel incorporating an advancing/retracting mechanism for advancing or retracting a driven member (e.g., a cam ring) while rotating the driven member.
2. Description of the Related Art
As a conventional advancing/retracting mechanism, incorporated in a photographing (imaging) lens barrel, for advancing or retracting a driven member such as a cam ring while rotating the driven member, an advancing/retracting mechanism which includes a rotatable ring driven to rotate by motor is known in the art. In this mechanism, the rotatable ring has a set of rotation transfer grooves extending parallel to the photographing optical axis while the drive member has a set of followers which are guided linearly along the photographing optical axis and engaged in the set of rotation transfer grooves, respectively. The set of followers are also engaged in a set of lead grooves formed on a non-rotatable advancing/retracting guide ring. Each lead groove of this advancing/retracting guide ring is inclined with respect to both a circumferential direction of the advancing/retracting guide ring and the direction of the rotational axis of the rotatable ring. Rotating the rotatable ring causes the set of followers of the driven member to move along the photographing optical axis of the rotatable ring with rotating due to both the engagement of the set of followers of the driven member with the set of rotation transfer grooves and the engagement of the followers of the driven member with the set of lead grooves of the advancing/retracting guide ring. In this known advancing/retracting mechanism, backlash between the set of followers and the set of lead grooves (guide grooves) must be removed so that the driven member can be driven to move along the photographing optical axis with a high degree of positioning accuracy in a ready-to-photograph state. However, a mechanism for removing such backlash is generally complicated.